Motor%20protection

Grundfos Motor Book

Grundfos Motor Book

Fusible sa\ue001ety switch \u201cQuick-acting\u201d \ue001uses \u201cTime-lag\u201d \ue001uses

Fuse clearing time

Thermal circuit breakers

Magnetic circuit breaker Circuit breaker rating

What overload relays do

Trip class designation

Calculation example TP designation Internal \ue001itting \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 Connection\ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u TP designation \ue001or the diagram\ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 Thermistors \u2013 also built into the windings \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0

How does a thermistor \ue001unction? \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 TP-designation \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \

Connection\ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ TP 111 protected motors

TP 211 protected motors

Internal protection devi PTC thermistors

What Grund\ue001os o\ue001\ue001ers?

\ u e 0 0 0 \ u e 0 0 0 \ u e 0

\ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0 \ u e 0 0 0

Grundfos Motor Book

Why is motor protection necessary?

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Why is motor protection

necessary?

In order to avoid unexpected breakdowns, costly repairs and subsequent losses due to motor

downtime, it is important that the motor is \ue001itted with some sort o\ue001 protective device\ue000 Generally speaking, motor protection can be divided into

the \ue001ollowing 3 levels:

\u2022\ue000External protection against short circuit in\ue000

the whole installation\ue000 External protection

device is normally di\ue001\ue001erent types o\ue001 \ue001uses or short circuit relays\ue000 This kind o\ue001 protection

device is compulsory and legal and placed under sa\ue001ety regulations\ue000

\u2022\ue000External protection against overload of spe-\ue000

cific equipment; i\ue000e\ue000 to avoid overload o\ue001 pump motor and thereby prevent damage

and breakdown o\ue001 the motor\ue000 This type o\ue001 protection reacts on current\ue000

\u2022\ue000Built-in motor protection with thermal\ue000

overload protection to avoid damage and

breakdown o\ue001 motor\ue000 The built-in protector always require an external circuit breaker

while some built-in motor protection types even require an overload relay\ue000

Fuse Circuit breaker Overload relay Built-in thermal protection

Overload accounts \ue001or some 30% o\ue001 all motor \ue001ailure Source: Electrical Research Association USA

What fault conditions are we

talking about?

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What fault conditions are we

talking about?

A wide range o aults can occur di erent places in the application There ore, it is important to anticipate the cause o events, and protect the motor against obstacles in the best possible way What ollows is a list o the most common

ault conditions where motor damage can be avoided by some sort o motor protection • Problems with the power supply quality:

– Overvoltage – Undervoltage

– Imbalanced voltages/currents – Frequency variation

• Installation, supply & motor ailures • Slowly developing temperature rise:

– Insu icient cooling

– High ambient temperature – High altitude operation – High liquid temperature

– Too high viscosity o the pumping liquid – Frequent starts

– Too big load inertia –(not common or pumps)

• Quickly developing temperature rises: – Locked rotor

– Phase breakage

To protect a circuit against overloads and short circuits, a circuit protective device must deter-mine when one o these ault conditions occurs It must then automatically disconnect the circuit

rom the power source A use is the simplest device or accomplishing these two unctions Normally uses are built together by means o a sa ety switch, which can switch o the circuit On the ollowing pages, we will present three types o uses as to their unction and to where they are used: Fusible sa ety switch, “quick-act-ing” use and “time-lag” use

Fusible sa ety switch Switch

Fuses Lack o ventilation due to dirt on the motor

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What fault conditions are we

talking about?

Fusible safety switch

A usible sa ety switch is a sa ety switch, which is combined with a use in a single enclosure The switch manually opens and closes the circuit, while the use protect against overcurrent protection Switches are generally used in connection with service when it is necessary to cut o the current, or in connection with ault situations

The sa ety switch is a switch, which is placed in a separate enclosure The enclosure protects personnel against accidental exposure to electri-cal connections and against exposure to weather conditions Some sa ety switches come with a built-in unction or uses, and some sa ety switches come without built-in uses, containing only a switch

The overcurrent protection device ( use) has to recognise the di erence between overcurrent and short circuit Slight overcurrents or example, can be allowed to continue or a short period o time But as the current magnitude increases, the protection device has to react quickly It is impor-tant to interrupt short circuits immediately

The usible disconnect switch is an example o a device which is used or overcurrent protection Properly sized uses in the switch open the circuit when an overcurrent condition occurs

“Quick-acting” fuses

Nontime-delay uses provide excellent short cir-cuit protection However, brie overloads, such as motor starting currents, may cause problems

or this kind o use There ore, nontime-delay uses are best used in circuits, which are not subject to large transient currents Normally, nontime-delay uses hold some 500% o their rated current or one- ourth o a second A ter this time, the current-carrying element melts, and opens the use Thus, in motor circuits, where the starting current o ten exceeds 500% o the use’s rated current, nontime-delay uses are not recommended

Switch

Fuses

Fuses are typically represented by these symbols in electrical circuit diagrams

Fusible sa ety switch

K

N

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M V

L 3

L 2

L 1

S 1

What fault conditions are we

talking about?

“Time-lag” fuses

This kind o use provides both overload and short-circuit protection Typically, they allow up to 5 times the rated current or up to 10 seconds and or shorter periods even higher currents Usually, this is su icient to allow a motor to start without opening the use On the other hand, i an overload condition occurs and persists or a longer period o time, the

use will eventually open

Fuse clearing time

The use clearing time is the response time it takes the use to open Fuses have an inverse time characteristic, meaning that the greater the overcurrent, the shorter the clearing time Generally speaking, pump motors have a very short run-up time; below 1 second So, blown

uses during start-up are normally not an issue or pumps i the uses match the motor’s ull-load currentand is a time-lag use

The illustration on your right-hand side shows the principle o a tripping curve or a use The x-axis shows the relation between the actual current and the ull-load current: I the motor consumes the ull-load current or less, the use does not trip But at 10 times the ull-load cur-rent, the use will trip in a very short time (0 01 s) The Y-axis shows the clearing time

During start-up, an induction motor consumes a large amount o current In some rare cases, this may lead to a cut-out via relays or uses Di erent methods o starting the motor exist in order to reduce the locked rotor current

Tripping curve or a “quick-acting” and a “time-lag” use

The “time-lag” use is the best choice or motors because o the high starting current

Clearing time o use

Less current - more time

More current - less time

Principle o a tripping curve or a use The graph shows the relation between the actual current and the ull-load current

10 100 I/In

10000

1

100

10

000

1

0 1

0 01

0 001

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Grundfos Motor Book

What is a circuit breaker and how

does it work?

What is a circuit breaker and how

does it work?

A circuit breaker is an overcurrent protection device It opens and closes a circuit automati-cally at a predetermined overcurrent When the circuit breaker is applied correctly within its rating, opening and closing the circuit breaker does not damage it

It is easy to reactivate the circuit breaker imme-diately a ter a overload has occurred The circuit breaker is simply reset a ter the ault is corrected We distinguish between two kinds o circuit breakers: Thermal and magnetic circuit breakers

Thermal circuit breakers

Thermal circuit breakers are the most reliable and cost-e ective type o protection device that exists and are well-suited or motors They can withstand high-level current waves, which arise

rom motor starts and they protect the motor against ailure e g locked rotor

Magnetic circuit breakers

Magnetic circuit breakers are precise, reliable and cost-e ective The magnetic circuit breaker is stable temperature-wise, meaning that it

is rarely a ected by changes in the ambient temperature

Compared to thermal circuit breakers, magnetic circuit breakers o er a more precise trip time The illustration on your right-hand side shows the characteristics o the two types o circuit breakers

Circuit breaker rating

Circuit breakers are rated according to the level o ault current they interrupt So, when you select a circuit breaker, always choose one that can sustain the largest potential short-circuit current, which is likely to occur in the application

Characteristics of thermal and magnetic circuit breakers

Thermal Magnetic

Temperature sensitive Not temperature sensitive

Not voltage sensitive Voltage sensitive

Fixed time delay Various time delays

Push-to-reset and switch unction Switch unction

Limited circuit unctions Variety o circuit unctions

Small package size Larger package size

Lower cost Higher cost

A circuit breaker is an overcurrent protection device It opens and closes a circuit automatically on a

predetermined overcurrent Subsequently, the circuit closes automatically or manually

What overload relays do

What overload relays do

Overload relays:

• Make it possible or the motor to handle harm-less temporary overloads without interrupting the circuit, i e motor starting

• Trip and open a motor circuit, i the current exceeds its limits and might damage the motor • Are reset either automatically or manually

once the overload situation has passed

IEC and NEMA are responsible or setting the stand-ards as to trip classes and thus or overload relays

Trip class designation

Generally, overload relays react to overload relay conditions according to the trip curve Regardless o the product style (NEMA or IEC), trip classes speci y the periode o time it takes the relay to open when overload occurs The most common classes are 10, 20 and 30 The igure re ers to the periode o time it takes the relay to trip A class 10 overload relay trips within 10 seconds or less at 600% o ull-load current, a class 20 overload relay trips within 20 seconds or less and a class 30 overload relay trips within 30 seconds or less The degree o inclination o the trip curve depends on the motor’s protection class IEC motors are typically adapted to the application in which they are designed to operate This implies that the overload relay is able to handle excess amounts o current, very close to its maximum capacity The trip time is the time it takes or a relay to trip dur-ing overload The trip time is divided into di erent classes The most common trip classes are 10, 20 and 30 Trip class 10 is the most common one or IEC motors because they are o ten adapted to the application NEMA motors are applied with more built-in excess capacity, and there ore, the trip class 20 is most common

Trip class 10 relays shut o the motor within 10 seconds at 600% o ull-load current Trip class 10 is normally used or pump motors because the run-up time o the motor is around 0 1 – 1 second Many high inertia industrial loads require more time to start Many o these loads require trip class 20

Class 30 Class 20 Class 10 100 200 400 800 1000 % o Full-load current 2 Hr 1 Hr 20 Min 10 Min 4 Min 2 Min 1 Min 30 Sec 20 Sec 10 Sec 4 Sec 2 Sec 1 Sec Trip time

The trip time is the time it takes or a relay to trip during over-load The trip time is divided into di erent classes

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What overload relays do

How to combine fuses with overload

relays

Fuses prevent short circuits rom damaging the installation and in worst case causing a ire, and must there ore have adequate capacities The lower currents are cleared by the overload relay Here, the rated current o the use does not correspond to the motor rating but to the current, which is likely to damage the weakest components in the installation As mentioned previously, the use provides short circuit pro-tection and does not provide low overcurrent protection

The illustration on your right-hand side shows the most important parameters that orm the basis or a success ul co-ordination o uses and overload relays

It is essential that the use trips out be ore ther-mal damage o other parts o the installation occur because o short-circuit

The most important parameters that orm the basis or a success ul co-ordination o uses and overload relays The

use time current curve always has to be situated lower than the limit curve (red curve) or thermal damage

Overload relay time curent characteristic Fuse time current characteristic

Cross over current

Limit of thermal damage to the overload relay time/current characteristic Current Tim e Full load current Motor current Starting current

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Advanced external motor

protection relays

Advanced external motor

protection relays

More advanced external motor protection systems can also protect against overvolt-age, phase imbalance, too many starts/stops, vibrations, PT100 temperature monitor-ing o stator and bearmonitor-ings, insulation resist-ance and monitor ambient temperature

Further, advanced external motor protection systems are able to handle the signal rom built-in thermal protection Thermal protection device will be covered later on in this chapter These external motor protection relays are designed to protect three-phase motors against conditions, which can damage them in the short or the long run In addition to motor protection, the external protection relay has eatures that can protect the motor in di erent situations:

• Give an alarm be ore damage results rom a

process mal unction

• Diagnose problems a ter a ault

• Allow veri ication o correct relay operation

during routine maintenance

• Monitor bearings or temperature and vibration

It is possible to connect overload relays through-out an entire plant to a central control system and constantly monitor and make a ast ault diagnose When an external protection relay in an overload relay is installed, the downtime decreases due to process problems The expla-nation is that it is possible to detect the ault quickly and avoid that it causes any damages to the motor

For instance, the motor can be protected against: • Overload

• Locked rotor

• Stall / mechanical jam • Repeated starts

• Open phase • Ground ault

• Overtemperature (using PT100 or

thermis-tors signal rom the motor) • Undercurrent

• Overload warning

Overload Short circuit Locked rotor

Stall / mechanical jam Repeated starts

Open phase / imbalance Ground ault

Overtemperature Undercurrent Overload warning

Advanced motor protection relay

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Advanced external motor

protection relays

Setting of external overload relay

The ull-load current at a given voltage indicated on the nameplate is normative or setting the overload relay Because o the variable voltages around the world, motors or pumps are made to be used at both 50 Hz and 60 Hz in a wide

volt-age range There ore, a current range is indicated on the motor’s nameplate The exact current

capacity can be calculated when we know the voltage

Calculation example

When we know the precise voltage or the installation, the ull-load current can be calculated at 254 ∆/440 Y V, 60 Hz

The data is indicated on the nameplate as shown on the illustration on your right-hand side

= 60 Hz U = 220-277 ∆/380 - 480 Y V I n = 5 70 - 5 00/3 30 - 2 90 A 60 Hz data calculation U_a = 254 ∆/440 Y V (actual voltage) U_min = 220 ∆/380 Y V

(Minimum values in the voltage range) U_max = 277 ∆/480 Y V

(Maximum values in the voltage range) The voltage ratio is determined by the ollowing equations:

The ull-load current at a given voltage indicated on the nameplate is normative or setting the overload relay Stop Auto/manual reset selector Full-load current Current setting 2 L1 L2 L3 _N 3 4

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Advanced external motor

protection relays

Calculation of the actual full-load current (I):

I = 5 70/3 30 A_min

(Current values or Delta and Star at minimum voltages)

I_max = 5 00/2 90 A

(Current values or Delta and Star at maximum voltages)

Now, it is possible to calculate the ull-load current by means o the frst ormula:

I or Delta values:

5 70 + (5 00 - 5 70) • 0 6 = 5 28 = 5 30 A I or Star values:

3 30 + (2 90 - 3 30) • 0 6 = 3 06 = 3 10 A The values or the ull-load current correspond to the permissible ull-load current o the motor at 254 ∆/440 Y V, 60 Hz

Rule-o -thumb: The external motor over-load relay is always set to the nominal current shown on the nameplate

However i motors are designed with a service actor, which is then shown on the nameplate eg 1 15, the set current or the overload relay can be raised by 15% compared to ull-load cur-rent or to the service actor amps, (SFA) which is normally indicated on the nameplate

I the motor is connected in star = 440 V 60 Hz the overload relay then has to be set to 3 1 A

2

L1 L2 L3 _N

3 4

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Internal protection

- built into the motor

Internal protection

- built into the motor

Why have built-in motor protection, when the motor is already itted with overload relays and

uses? Sometimes the overload relay does not register a motor overload Here are a couple exampels o this:

• I the motor is covered and is slowly warmed up to a high damaging temperature

• In general, high ambient temperature

• I the external motor protection is set at a too high trip current or is installed in a wrong way • I a motor, within a short period o time,

is restarted several times, the locked rotor current warms up the motor and eventually damages it

The degree o protection that an internal pro-tection device provides is classi ied in the IEC 60034-11 standard

TP designation

TP is the abbreviation or thermal protection

Di erent types o thermal protection exist and are identi ied by a TP-code (TPxxx) which indicates: • The type o thermal overload or which the

thermal protection is designed (1 digit)

• The numbers o levels and type o action (2 digit)

• The category o the built-in thermal protec-tion (3 digit)

When it comes to pump motors, the most com-mon TP designations are:

TP 111: Protection against slow overload

TP 211: protection against both rapid and slow overload

Built-in thermal protection

Internal protection built into windings

Indication o the permissible temperature level

when the motor is exposed to thermal overload Category 2 allows higher temperatures than category 1 does

Internal protection

- built into the motor

All Grund os single-phase motors have current and temperature-dependent motor protection in accordance with IEC 60034-11 The motor protection is o the TP 211 type, which reacts to both slow and quick-rising temperatures The device is automatically reset

3-phase MG Grund os motors as rom 3 0 kW have PTC as standard These motors have been tested and are approved as TP 211 motors, which react to both slow and quick-rising tempera-tures

Other motors used or Grund os pumps (MMG model D and model E, Siemens, Baldor etc ) can be TP 211 but are normally TP 111 Nameplate designation should always be ollowed

In ormation about which type o protection has been applied to a motor can be ound on the nameplate using a TP (thermal protection) designation according to IEC 60034-11

In general, internal protection can be imple-mented using two types o protectors: Thermal protectors thermistors.or

Thermal protectors - built into the

ter-minal box

Thermal protectors or thermostats use a snap-action, bi-metallic, disc type switch to open or to close the circuit when it reaches a cer-tain temperature Thermal protectors are also re erred to as Klixons, (trade name rom Texas Instruments)

When the bi-metal disc reaches a predetermined temperature, it opens or closes a set o contacts in an energized control circuit Thermostats are available with contacts or normally open or normally closed operation, but the same device cannot be used or both Thermostats are pre-calibrated by the manu acturer and cannot be adjusted The discs are hermetically sealed and are placed on the terminal board

TP 211 in a MG 3 0 kW motor equipped with PTC 3~MOT MG 100LB2-28FT130-C2 TP 211 P 3,002 kW No85815810 85 8 1 5 8 1 0 U 380-415D V 1/1 I 6,25 A max I 6,85 A Eff.% 82 n 288-2910 m ni cos 0.88-0.82

50 Hz

TP 111 in a Grund os MMG 18 5 kW motor equipped with PTC

Thermal switch without heater Thermal switch with heater

Thermal switch without heater or three-phase motors

(star-point protector)

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Internal protection

- built into the motor

A thermostat can either energize an alarm cir-cuit, i normally open, or de-energize the motor contactor, i normally closed and in series with the contactor Since thermostats are located on the outer sur ace o the coil ends, they sense the temperature at that location In connection with three-phase motors, thermostats are considered unstable protection against stall or other rap-idly changing temperature conditions In single phase motors thermostats do protect against locked-rotor conditions

Thermal switch - built into the

windings

Thermal protectors can also be built into the windings, see the illustration on your right-hand side

They operate as a sensitive power cut-out or both single and three-phase motors In single-phase motors, up to a given motor size around 1 1 kW it can be mounted directly in the main circuit to serve as an on-winding protector

Klixon and Thermik are examples o thermal switch These devices are also called PTO (Protection

Thermique à Ouverture)

Internal fitting

In single-phase motors one single thermal

switch is used In three-phase motors 2 thermal switches connected in series are placed between the phases o the motor In that way all three phases are in contact with a thermal switch Thermal switches can be retro itted on the coil end, but the result is an increased reaction time The switches have to be connected to an exter-nal monitoring system In that way the motor is protected against a slow overload The thermal switches do not require an ampli ier relay Thermal switches CANNOT protect against locked- rotor conditions

Thermal protection built into the windings

Current and temperature sensitive thermal switches Two thermal switches

connected in series with thermal sur ace contact on all three phases

Klixons

Thermik - PTO

Thermal protection to be connected

in series with the winding or to a control circuit in the motor

How does a thermal switch

function?

How does a thermal switch

function?

The curve on your right-hand side shows the resistance as a unction o the temperature

or a typical thermal switch Depending on the thermal switch manu acturer, the curve changes T is typically around 150 - 160°C_N

Connection

Connection o a three-phase motor with built-in thermal switch and overload relay

TP designation for the diagram

Protection according to the IEC 60034-11 stand-ard: TP 111 (slow overload) In order to handle a locked-rotor, the motor has to be itted with an overload relay 3 M K1 MV K1 N L3 L2 L1 K1 N S1 K1 S1 S2 MV MV R [ ] -5 +5 8 [ C ]˚ TN

Resistance as a unction o the tem-perature or a typical thermal switch

Automatic reclosing Manual reclosing

S1 On/o switch S2 O switch K1 Contactor

t Thermal switch in motor M Motor

MV Overload relay

Thermal switches can be loaded as ollowed: U = 250 V AC

IN = 1 5 A

max

Imax = 5 0 A (cut-in and cut-out current)

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How does a thermal switch

function?

Thermistors

- also built into the windings

The second type o internal protection is the thermistors or Positive Temperature Coe icient sensors (PTC) The thermistors are built into the motor windings and protect the motor against locked-rotor conditions, continuous overload and high ambient temperature Thermal protection is then achieved by monitoring the temperature o the motor windings with PTC sensors I the windings exceed the rated trip temperature, the sensor undergoes a rapid change in resistance relative to the change in temperature

As a result o this change, the internal relays de-energize the control coil o the external line break contactor As the motor cools and an acceptable motor winding temperature has been restored, the sensor resistance decreases to the reset level At this point, the module resets itsel automatically, unless it was set up

or manual reset

When the thermistors are retro itted on the coil ends, the thermistors can only be classi ied as TP 111 The reason is that the thermistors do not have complete contact with the coil ends, and there ore, it cannot react as quickly as it would i they were itted into the winding originally The thermistor temperature sensing system

consists o positive temperature coe icient sen-sors (PTC) embedded in series o three - one

between each phase - and a matched solid-state electronic switch in an enclosed control mod-ule A set o sensors consists o three sensors, one per phase The resistance in the sensor remains relatively low and constant over a wide temperature band and increases abruptly at a pre-determined temperature or trip point

When this occurs, the sensor acts as a solid-state thermal switch and de-energizes a pilot relay The relay opens the machine’s control circuit to shut down the protected equipment When the winding temperature returns to a sa e value, the module permits manual reset

PTC sensors

3 PTC sensors; one in each phase

PTC protection built into windings

The colours on the PTC leads help determine what trip temperature the PTC sensor is made to handle This speci ic PTC sensor has a T at 160°C PTC sensors come with trip temperatures ranging orm 90°C to 180°C with an interval o 5 degrees

NF

Thermistor / PTC Only temperature sensitive The thermistor has to be connected to a control circuit, which can convert the resistance signal, which again has to disconnect the motor Used in three-phase motors

+T

white black blue blue blue white black black black red green

How does a thermistor function?

Thermistors are standard in all Grund os motors rom 3 kW and up

The positive temperature coe icient (PTC) ther-mistor system is considered ail-sa e since a bro-ken sensor or sensor lead results in an in inite resistance and develop a response identical to that o elevated temperature, de-energizing the pilot relay

How does a thermistor function?

The critical values o the resistance / tempera-ture char-acteristic or motor-protection sen-sors are de ined by the DIN 44081/DIN 44082 standards

The DIN curve on your right shows the resist-ance in the thermistor sensor as a unction o temperature

The thermistor has the ollowing advantages compared to the PTO:

• Reacts aster because o lower volume and mass

• Better contact with the winding • Sensors on each phase

• Provide protection against locked-rotor con-ditions

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Typical resistance versus temperature charac-teristic o a PTC thermistor (DIN 44081/44082)

Critical limits in the resistance temperature charac-teristic or motor protection sensors

T = tripping temperature or the thermistor The curves covers one thermistor unit

NAT

Values must be trippled to cover the motor PTC thermistors

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TP designation

TP designation

The TP 211 motor protection can only be achieved when PTC thermistors are entirely incorporated in the coil end TP 111 protection is only achieved in connection with retro itting The motor must be tested and approved by the manu acturer in order to obtain the TP 211 designation I a motor with PTC thermistors is TP 111 protected, it has to be itted with an overload relay in order to handle blocking

Connection

The igures on your right hand side show a connection o a three-phase motor with PTC thermistors and Siemens tripping unit In order to obtain protection against both slow and rapid overload, we recommend the ollowing type o connection or motors with PTC sensor and TP 211 and TP 111 protection

TP 111 protected motors

I the motor with the thermistor is marked with TP 111, it means that the motor is only protected against slow overload In order to protect the motor against rapid overload, the motor has to have a motor overload realy The overload relay has to be connected to the PTC relay in series

TP 211 protected motors

The TP 211 motor protection can only be

achieved when the PTC thermistors is entirely incorporated in the coil end TP 111 protection is achieved in connection with retro itting

The thermistors are designed in accordance with the DIN 44082 standard, and can handle a load U o 2 5 VDC All tripping units are designed to_max receive signals rom DIN 44082 thermistors, i e thermistors rom Siemens

Please note: It is important that the built-in

PTC device is connected to the overload relay in series Reclosing o an overload relay over and over again, can lead to winding burnout, i the motor is blocked or starts with high inertia There ore, it is important to ensure that both the PTC device and the overload relay indicate that the temperature and the consumption o current is normal This is done by connecting the

98 96 A2 T2 T1 K1 S1 K H2 95 A1 H1 3UN2 100-0 C N 3 M K1 N L3 L2 L1 K1 K1 S1 S2 98 96 A2 T2 T1 K1 S1 K H2 95 A1 H1 3UN2 100-0 C N 3 M K1 N L3 L2 L1 K1 K1 S1 MV MV S2 MV

Automatic reclosing Manual reclosing Automatic reclosing Manual reclosing TP 111 protected motors TP211 protected motors S1 On/o switch K1 Contactor t Thermistor in motor M Motor

MV Motor overload relay

3UN2 100-0C tripping unit with automatic reclosing: A Ampli ying relay

C Output relay H1 LED “Ready” H2 LED “Tripped”

A1, A2 Connection or control voltage T1, T2 Connection or thermistor circuit

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What have you learned about

motor protection?

PT100 – temperature sensor

The PT100 is a protection device The PT100 var-ies its resistance continuously and increasingly as the temperature changes A signal rom a PT100 temperature sensor can be used or eed-back control by a microprocessor to determine the exact winding temperature This can also be used to monitor bearing temperatures

What have you learned about

motor protection?

There are several methods to protect an electric motor rom overheating What ollows is a sum-mary o the most important devices and their characteristics

External protection devices

External protection devices such as uses, cir-cuit breakers and thermal and current overload relays, react on the current drawn by the motor External protection device is set to shut the motor down i the current exceeds the nominal

ull load There ore, the motor may overheat without registering a problem, e g i the an cover inlet gets blocked by a plastic bag or by an excessively high ambient temperature, the current will not increase, but the temperature will External protection devices protect against a locked-rotor situation

Internal protection devices

Internal protection devices such as thermistors, are much more e ective than external

protection devices The reason is that internal protection device actually measures the winding temperature The two most common internal protection devices are PTC - thermistors and PTO - thermal switches

External motor protection

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Grundfos Motor Book

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What have you learned about

motor protection?

PTC thermistors

PTC thermistors, (Positive Temperature Coe i-cient thermistors) can be itted into the wind-ings o a motor during production or retro itted a terwards Usually three PTC thermistors are

itted in series; one in each phase o the wind-ing They can be purchased with trip tempera-tures ranging rom 90°C to 180°C in 5° steps PTC thermistors have to be connected to a thermis-tor relay, which detects the rapid increase in resistance o the thermistor when it reaches its trip temperature These devices are non-linear At ambient temperatures the resistance o a set o three will be about 200 ohms, and this will increase rapidly to 3000 ohms, (1000 ohms each) I the temperature increases any urther, the PTC thermistor can reach several thousand ohms The thermistor relays are usually set to trip at 3000 ohms or are preset to trip according to what the DIN 44082 standard prescribes

Thermal switch and thermostats

Thermal switches are small bimetallic switches that switch due to the temperature They are available with a wide range o trip temperatures; normally open and closed types The most

common type is the closed one, one or two, in series, are usually itted in the windings like thermistors and can be connected directly to the circuit o the main contactor coil In that way no relay is necessary This type o protection is cheaper than thermistors, but on the other

hand, it is less sensitive and is not able to detect a locked rotor ailure

PTC sensors

Three PTC sensors; one in each phase

PTC protection built into windings

Current and temperature sensitive thermal switches Klixons

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What Grundfos offers?

What Grundfos offers?

All Grund os’ single-phase motors and all three-phase motors above 3 kW come with built-in thermal protection Motors with PTC sensors come with three PTC sensors, one in each phase This is mainly or protection against slowly ris-ing temperatures in the motor, but also or protection against rapidly rising temperatures Depending on the motor construction and its application, the thermal protection may also serve other purposes or prevent harm ul tem-peratures in the controllers, which are placed on the motors

There ore, i the pump motor has to be protected against any conceivable situation, the motor has to be itted with both an overload relay and a PTC device i the motor is not TP 211 protected An overload relay and the PTC have to be con-nected in series, so that the motor does not

restart be ore the both devices are ready In this way the motor is not overloaded or too warm Grund os recommends using the standard

equipped thermistors or motors The client and the electrician have to install a PTC-relay that complies with the DIN 44082 standard In that way, the built-in thermistors are used as a stand-ard protection device in 3 kW motors

Thermistor / PTC Only temperature sensitive The thermistor has to be connected to a control circuit, which can convert the resistance signal, which again has to disconnect the motor Used in three-phase motors

+T

PTC sensors

Three PTC sensors; one in each phase